1. Field of the Invention
The invention relates to a measuring device for measuring the envelope power and the mean-power value of a high-frequency signal.
2. Discussion of the Background
A measuring device is known from DE 199 55 342 A1. With the measuring device disclosed in this specification, it is possible to measure both the envelope power and also the mean-power or RMS (root mean square) value. To cover the maximum possible dynamic range, the measurement range is divided into several subdivisions, which are allocated respectively to several measurement branches arranged parallel to one another. A chopper is disposed in each measurement branch, both of which are controlled synchronously. Furthermore, an analog/digital converter, which is supplied with a synchronous clock-pulse rate, is arranged in each measurement branch. After a weighted addition of the digitized measured signals of the individual measurement branches, a synchronous demodulation is implemented before the signal is evaluated.
The disadvantage of the measuring device known from DE 199 55 342 A1 is the use of parallel measurement branches, as a result of which the measuring device suffers from an extremely complex design. Alongside the synchronization of the choppers and the analog/digital converters, it must also be ensured that the group delay time of the measured signal is exactly equal in all measurement branches. In practice, this causes problems, especially with regard to video bandwidths to be realized within the order of magnitude of 30 MHz. With a single-path realization of the measuring device, it must be ensured that the analog/digital converter is not overdriven at the upper end of the dynamic range. This leads to a relatively poor signal level at the lower end of the dynamic range. Accordingly, special measures must be implemented to guarantee a good measurement accuracy.